1. Field of the Invention
The present invention relates to hydraulic systems for controlling the operation of valves. This invention more specifically relates to a control system utilized to control a retainer valve in an underwater well test system.
2. Background Art
U.S. Pat. No. 4,693,315 to Frank H. Taylor discloses a well test system which includes a hydraulically controlled retainer valve in the upper section of the test pipe string.
An electro/hydraulic control system for controlling remotely located valves is disclosed in U.S. Pat. No. 4,636,934, which is incorporated herein for reference. This elaborate system controls a number of remote valves in a well test system for underwater wells. The control system also measures various well parameters and analyzes the measurements for preprogrammed considerations to control remotely located valves for optimum operation of the test system.
Retainer valves are used above a subsea test tree in the upper section of the string of pipe lowered into a well to conduct formation evaluating flow tests.
Before starting test operations in a well, the retainer valve is usually closed to seal pressure from above and permit all test string connections from the retainer valve to surface to be pressure tested. After pressure testing, retainer valves are reopened to permit flow through the test string while testing.
The primary function of the retainer valve is to close before the upper section of the test string is quickly disconnected from the rest of the test string during emergency conditions. The closed retainer valve retains water polluting liquids in the upper test string section and prevents discharge of these liquids into surrounding water. The closed retainer valve also prevents discharge of pressurized fluids downward from the upper test string section on disconnect with possible resulting rapid jet assisted upward movement of the string section which could cause injury or property damage.
Previous hydraulic control systems included control conduits connected to a pressure source on the surface. These conduits extended from the surface pressure source possibly thousands of feet downwardly to conduct pressured fluid to valves in well test strings to open or close the valves as required during well test operations. Because of the long lengths and small size of these conduits, along with high viscosity of pressurized control liquids pumped through the conduits, liquids in sufficient quantities necessary to close or open hydraulically operated valves require long periods of time to travel from surface to a valve and operate the valve. As retainer valves are sometimes closed because of emergency conditions which develop during well testing, quick closure is very desirable.